The present invention relates to a tilting mechanism for the optical pickup unit of an optical information record/playback apparatus such as a video disk player.
The angle of irradiation of laser light upon the surface of a disk and the focusing of the laser light onto the surface of the disk need to be accurately controlled during the reading of information from the disk by an optical information record/ playback apparatus or the like. However, since the disk warps due to its own weight when placed on the apparatus so that the peripheral portion of the disk sags the angle of irradiation of the laser light and the focusing thereof cannot be accurately controlled simply by horizontally moving the optical pickup of the apparatus in the radial direction of the disk. Therefore, a conventional tilting mechanism, as shown in FIG. 5, is provided for the optical pickup unit of the apparatus.
As shown in FIG. 5, the optical pickup unit has a support member 30 for supporting a sliding shaft 30a at both the ends thereof. The support member 30 is borne at a fulcrum 0 on a base 20 on which a spindle motor 10 is mounted. The optical pickup 40 of the pickup unit is supported on the sliding shaft 30a so that the pickup can be slid in the radial direction of the disk 50 as shown by double headed arrow A in FIG. 5.
When the disk 50 is placed on the spindle motor 10, the distance between the surface of the disk and the base 20 decreases toward the peripheral edge of the disk. In other words, the peripheral portion of the disk 50 inclines or sags toward the base 20. Thus, the angle of the disk 50 to the pickup 40 is detected by an angle sensor attached to the pickup, to perform tilting servocontrol to gradually tilt the support member 30 toward the base 20 as the pickup is slid on the sliding shaft 30a toward the peripheral edge of the disk. The angle of the disk 50 to the pickup 40 is thus kept zero. At the same time, the distance between the disk 50 and the pickup 40 is kept nearly constant. The error in the distance, which takes place because the correction of the angle of the disk 50 to the pickup 40 is performed with priority over the correction of the distance between them, is corrected by a focusing servocontrol based on a focusing error signal. Therefore, a focusing actuator for moving an objective lens has a greater load if the error in the distance is larger.
When the pickup 40 is located between the fulcrum 0 of the support member 30 and the center of the disk 50 as shown by P in FIG. 5, the distance between the pickup 40 and the disk 50 is decreased as the pickup is tilted by the tilting servocontrol so as to improve the angle of the disk to the pickup. Thus, the focusing actuator has a still greater load to such an extent that the apparatus cannot perform playback from the disk 50 if the capacity of the focusing actuator is small.
Since the correlation between the angle of each of many disks to the pickup 40 and the distance between each of the disks and the pickup is examined to predetermine the position of the fulcrum 0 of the conventional tilting mechanism to substantially, accurately control the angle and the distance for a typical disk, it is likely that the focusing actuator cannot follow-up a disk which causes an improper correlation such as a disk that is warped in the central portion thereof as shown in FIG. 6. Therefore, the apparatus cannot perform playback from such a warped disk.